The invention relates to an automatic shut-off and indication device for an electric heating appliance comprising: means for sensing usage of the appliance and for providing a usage-signal indicating a non-usage of the appliance; means for off-switching a heater of the appliance in response to a switching signal derived from the usage-signal; means for sensing orientation of the appliance and for providing an orientation signal for indicating different orientations of the appliance; and means for activating an indicator in response to the switching signal, the indicator signalling the off-switching of the heater.
The invention further relates to an electric pressing iron comprising such a device.
Such a device and iron are known, for instance, from U.S. Pat. No. 4,203,101. Automatic shut-off (ASO) systems for electric heating appliances, particularly for electric pressing irons are known. A sensor, for example a motion sensor with a mercury switch or a hand sensor monitors whether the pressing iron is being used or not. The ASO system switches off the electrical heater of the iron when the iron is not used for a certain period in order to avoid a hazardous situation when the iron is left unattended. The indicator warns the user that the heating element is switched off. The indicator can be a visual one, for example a lamp or an audible one, for example a buzzer. When the user starts again using the iron, the ASO system switches on the heater of the iron. Usually, pressing irons can be left unattended in a substantial horizontal position or in a substantial vertical or heel rest position. Especially in the vertical position the indication can be irritating to the user if the time-out period is rather short, e.g. 30 seconds.
It is an object of the present invention to provide an improved ASO system for electric heating appliances. According to the invention the automatic shut-off and indication device as specified in the opening paragraph is characterized by means for providing a time delay between off-switching the heater and activating the indicator, which time delay is dependent on the orientation signal.
By providing a separate time delay for the activation of the indicator which is dependent on the orientation of the appliance it is achieved that the heater is always switched off at a moment which provides maximum safety, while the indicator is activated at an instant after switching off only when it makes sense to remind the user that the appliance is still connected to the mains. Particularly for pressing irons it is very convenient to provide that the time delay is shorter when the orientation signal indicates a substantial horizontal orientation of the appliance than the time delay in case the orientation signal indicates a substantial vertical position of the appliance. The time delay in the horizontal orientation may be zero to inform the user immediately of a very unsafe situation. The time delay in the vertical position can be much longer to accommodate for the usual intervals in the heel rest position during the ironing when the user would be irritated by the repeated operation of the indicator.
The means for sensing usage may comprise a motion sensor in a suitable place inside the appliance or a hand sensor in the handgrip of the appliance. In a preferred embodiment of the automatic shut-off and indication device, the means for providing a time delay comprises an indication timer for providing a delayed activation signal in response to the usage-signal and in the means for activating the indicator comprises: means for receiving the switching signal, the delayed activation signal and the orientation signal; and means for selecting one signal out of the switching signal and the delayed activation signal in response to predetermined values of the orientation signal. In this embodiment a selection is made between an immediate indication and a delayed indication depending on the orientation of the appliance after switch-off of the heater.
The heater may be switched off either immediately after the occurrence of the non-usage signal or after a certain delay provided by a switch-off timer which delays the response of the switching signal to the non-usage signal, for example for 30 seconds. In this way a time-out is created between the instant of detecting non-usage and the instant of switch-off of the heater. After off-switching of the heater, the indicator is activated after the lapse of a time period which depends on the orientation of the appliance. In case of a pressing iron this time period can be, for instance, zero seconds in the horizontal position and several minutes in the vertical position. This means that, when the heater is shut off after a certain time-out, the indicator is activated immediately in the horizontal position and activated delayed in the vertical position.
The automatic shut-off and indication device is particularly useful in electric pressing irons, but implementation in other electric heating appliances, such as water cookers, kettles, hair dryers and other hand-held or stationary heating appliances is possible as well.